Silicone polymer insulation film on semiconductor substrate and method for forming the film

ABSTRACT

A siloxan polymer insulation film has a dielectric constant of 3.3 or lower and has —SiR 2 O— repeating structural units. The siloxan polymer has dielectric constant, high thermal stability and high humidity-resistance on a semiconductor substrate. The siloxan polymer is formed by directly vaporizing a silicon-containing hydrocarbon compound expressed by the general formula Si α O β C x H y  (α, β, x, and y are integers) and then introducing the vaporized compound to the reaction chamber of the plasma CVD apparatus. The residence time of the source gas is lengthened by reducing the total flow of the reaction gas, in such a way as to form a siloxan polymer film having a micropore porous structure with low dielectric constant.

This is a continuation of U.S. patent application Ser. No. 09/243,156,filed Feb. 2, 1999, now abandoned which claims priority based onJapanese patent application No. 37929/1998, filed Feb. 5, 1998. Theentire disclosure of the parent application is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a semiconductor technique and moreparticularly to a silicone polymer insulation film on a semiconductorsubstrate and a method for forming the film by using a plasma CVD(chemical vapor deposition) apparatus.

2. Description of Related Art

Because of the recent rise in requirements for the large-scaleintegration of semiconductor devices, a multi-layered wiring techniqueattracts a great deal of attention. In these multi-layered structures,however, capacitance among individual wires hinders high-speedoperations. In order to reduce the capacitance it is necessary to reducethe dielectric constant (relative permittivity) of the insulation film.Thus, various materials having a relatively low dielectric constant havebeen developed for insulation films.

Conventional silicon oxide films SiO_(x) are produced by a method inwhich oxygen O₂ or nitrogen oxide N₂O is added as an oxidizing agent toa silicon material gas such as SiH₄ or Si(OC₂H₅)₄ and then processed byheat or plasma energy. Its dielectric constant is about 4.0.

Alternatively, a fluorinated amorphous carbon film has been producedfrom C_(x)F_(y)H_(z) as a material gas by a plasma CVD method. Itsdielectric constant ε is as low as 2.0-2.4.

Another method to reduce the dielectric constant of insulation film hasbeen made by using the good stability of Si—O bond. A silicon-containingorganic film is produced from a material gas under low pressure (1 Torr)by the plasma CVD method. The material gas is made from P-TMOS (phenyltrimethoxysilane, formula 1), which is a compound of benzene andsilicon, vaporized by a babbling method. The dielectric constant ε ofthis film is as low as 3.1.

A further method uses a porous structure made in the film. An insulationfilm is produced from an inorganic SOG material by a spin-coat method.The dielectric constant ε of the film is as low as 2.3.

However, the above noted approaches have various disadvantages asdescribed below.

First, the fluorinated amorphous carbon film has lower thermal stability(370° C.), poor adhesion with silicon-containing materials and alsolower mechanical strength. The lower thermal stability leads to damageunder high temperatures such as over 400° C. Poor adhesion may cause thefilm to peel off easily. Further, the lower mechanical strength canjeopardize wiring materials.

Oligomers that are polymerized using P-TMOS molecules do not form alinear structure in the vapor phase, such as a siloxane structure,because the P-TMOS molecule has three O—CH₃ bonds. The oligomers havingno linear structure cannot form a porous structure on a Si substrate,i.e., the density of the deposited film cannot be reduced. As a result,the dielectric constant of the film cannot be reduced to a desireddegree.

In this regard, the babbling method means a method wherein vapor of aliquid material, which is obtained by having a carrier gas such as argongas pass through the material, is introduced into a reaction chamberwith the carrier gas. This method generally requires a large amount of acarrier gas in order to cause the material gas to flow. As a result, thematerial gas cannot stay in the reaction chamber for a sufficient lengthof time to cause polymerization in a vapor phase.

Further, the SOG insulation film of the spin-coat method has a problemin that the material cannot be applied onto the silicon substrate evenlyand another problem in which a cure system after the coating process iscostly.

Object of the Invention

It is, therefore, a principal object of this invention to provide animproved insulation film and a method for forming it.

It is another object of this invention to provide an insulation filmthat has a low dielectric constant, high thermal stability, highhumidity-resistance and high adhesive strength, and a method for formingit.

It is a further object of this invention to provide a material forforming an insulation film that has a low dielectric constant, highthermal stability, high humidity-resistance and high adhesive strength.

It is a still further object of this invention to provide a method foreasily forming an insulation film that has a low dielectric constantwithout requiring an expensive device.

SUMMARY OF THE INVENTION

One aspect of this invention involves a method for forming an insulationfilm on a semiconductor substrate by using a plasma CVD apparatusincluding a reaction chamber, which method comprises a step of directlyvaporizing a silicon-containing hydrocarbon compound expressed by thegeneral formula Si_(α)O_(β)C_(x)H_(y) (α,β, x, and y are integers) andthen introducing it to the reaction chamber of the plasma CVD apparatus,a step of introducing an additive gas, the flow volume of which issubstantially reduced, into the reaction chamber and also a step offorming an insulation film on a semiconductor substrate by plasmapolymerization reaction wherein mixed gases made from the vaporizedsilicon-containing hydrocarbon compound as a material gas and theadditive gas are used as a reaction gas. It is a remarkable feature thatthe reduction of the additive gas flow also results in a substantialreduction of the total flow of the reaction gas. According to thepresent invention, a silicone polymer film having a micropore porousstructure with low dielectric constant can be produced.

The present invention is also drawn to an insulation film formed on asemiconductor substrate, and a material for forming the insulation film,residing in the features described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a plasma CVD apparatus usedfor forming an insulation film of this invention.

FIG. 2 is a graph showing the relationship between dielectric constantand the total flow of a reaction gas as well as the relationship betweenresidence time and the total flow of a reaction gas, both in experimentsusing PM-DMOS as a material gas.

FIG. 3 is a graph showing the relationship between the residence timeand dielectric constant in experiments using PM-DMOS as a material gas.

FIG. 4 is a graph showing the thermal desorption spectra of componentshaving a molecular weight of 16 due to desorption of CH₄ from films(PM-DMOS, DM-DMOS) according to the present invention in a thermaldesorption test.

FIG. 5 is a graph showing changes in the degree of vacuum correspondingto the number of total molecules dissociated from the films (PM-DMOS,DM-DMOS), i.e., pressure raises due to gas dissociated from the films inthe thermal desorption test.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Basic Aspects

In the present invention, the silicon-containing hydrocarbon compoundexpressed as the general formula Si_(α)O_(β)C_(x)H_(y) (α,β, x, and yare integers) is preferably a compound having at least one Si—O bond,two or less O—C_(n)H_(2n+1) bonds and at least two hydrocarbon radicalsbonded with silicon (Si). More specifically, the silicon-containinghydrocarbon compound includes at least one species of the compoundexpressed by the chemical formula (2) as follows:

wherein R1 and R2 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, and m and nare any integer.

Except for the species indicated above, the silicon-containinghydrocarbon compound can include at least one species of the compoundexpressed by the chemical formula (3) as follows:

wherein R1, R2 and R3 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, and nis any integer.

Except for those species indicated above, the silicon-containinghydrocarbon compound can include at least one species of the compoundexpressed by the chemical formula (4) as follows:

wherein R1, R2, R3 and R4 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, andm and n are any integer.

Further, except for those species indicated above, thesilicon-containing hydrocarbon compound can include at least one speciesof the compound expressed by the chemical formula (5) as follows:

wherein R1, R2, R3, R4, R5 and R6 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ andC₆H₅, and the additive gases are argon (Ar), Helium (He) and eithernitrogen oxide (N₂O) or oxygen (O₂).

Furthermore, except for those species indicated above, thesilicon-containing hydrocarbon compound can include at least one speciesof the compound expressed by the chemical formula (6) as follows:

wherein R1, R2, R3 and R4 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, andthe additive gases are argon (Ar), Helium (He) and either nitrogen oxide(N₂O) or oxygen (O₂).

Still further, the material gas can include at least one of saidsilicon-containing hydrocarbon compounds indicated above.

In accordance with another aspect of this invention, an insulation filmis formed on a substrate and the film is polymerized with plasma energyin a plasma CVD apparatus by using a material gas including asilicon-containing hydrocarbon compound expressed by formula 2.

Additionally, the insulation film is formed on a substrate and the filmis polymerized with plasma energy in a plasma CVD apparatus by using amaterial gas including a silicon-containing hydrocarbon compoundexpressed by formula 3.

Further, the insulation film is formed on a substrate and the film ispolymerized with plasma energy in a plasma CVD apparatus by using amaterial gas including a silicon-containing hydrocarbon compoundexpressed by formula 4.

Furthermore, the insulation film is formed on a substrate and the filmis polymerized with plasma energy in a plasma CVD apparatus by using amaterial gas including a silicon-containing hydrocarbon compoundexpressed by formula 5.

Still further, the insulation film is formed on a substrate and the filmis polymerized with plasma energy in a plasma CVD apparatus by using amaterial gas including a silicon-containing hydrocarbon compoundexpressed by formula 6.

In accordance with a further aspect of this invention, a material forforming an insulation film is supplied in a vapor phase in the vicinityof a substrate and is treated in a plasma CVD apparatus to form theinsulation film on the substrate by chemical reaction, and the materialis further expressed by formula 2.

Additionally, a material for forming an insulation film is supplied in avapor phase in the vicinity of a substrate and is treated in a plasmaCVD apparatus to form the insulation film on the substrate by chemicalreaction, and the material is further expressed by formula 3.

Further, a material for forming an insulation film is supplied in avapor phase in the vicinity of a substrate and is treated in a plasmaCVD apparatus to form the insulation film on the substrate by chemicalreaction, and the material is further expressed by formula 4.

Furthermore, a material for forming an insulation film is supplied in avapor phase with either nitrogen oxide (N₂O) or oxygen (O₂) as anoxidizing agent in the vicinity of a substrate and is treated in aplasma CVD apparatus to form said insulation film on said substrate bychemical reaction, and this material can be the compound expressed byformula 5.

Still further, a material for forming an insulation film is supplied ina vapor phase with either nitrogen oxide (N₂O) or oxygen (O₂) as theoxidizing agent in the vicinity of a substrate and is treated in aplasma CVD apparatus to form said insulation film on said substrate bychemical reaction, and this material further can be the compoundexpressed by formula 6.

Residence Time and Gas Flow

The residence time of the reaction gas is determined based on thecapacity of the reaction chamber for reaction, the pressure adapted forreaction, and the total flow of the reaction gas. The reaction pressureis normally in the range of 1-10 Torr, preferably 3-7 Torr, so as tomaintain stable plasma. This reaction pressure is relatively high inorder to lengthen the residence time of the reaction gas. The total flowof the reaction gas is important to reducing the dielectric constant ofa resulting film. It is not necessary to control the ratio of thematerial gas to the additive gas. In general, the longer the residencetime, the lower the dielectric constant becomes. The material gas flownecessary for forming a film depends on the desired deposition rate andthe area of a substrate on which a film is formed. For example, in orderto form a film on a substrate [r(radius)=100 mm] at a deposition rate of300 nm/min, at least 50 sccm of the material gas is expected to beincluded in the reaction gas. That is approximately 1.6×10² sccm per thesurface area of the substrate (m²). The total flow can be defined byresidence time (Rt). When Rt is defined described below, a preferredrange of Rt is 100 msec≦Rt, more preferably 200 msec≦Rt≦5 sec. In aconventional plasma TEOS, Rt is generally in the range of 10-30 msec.

Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F

wherein:

Pr: reaction chamber pressure (Pa)

Ps: standard atmospheric pressure (Pa)

Tr: average temperature of the reaction gas (K)

Ts: standard temperature (K)

r_(w): radius of the silicon substrate (m)

d: space between the silicon substrate and the upper electrode (m)

F: total flow volume of the reaction gas (sccm)

In the above, the residence time means the average period of time inwhich gas molecules stay in the reaction chamber. The residence time(Rt) can be calculated at Rt=αV/S, wherein V is the capacity of thechamber (cc), S is the volume of the reaction gas (cc/s), and α is acoefficient determined by the shape of the reaction chamber and thepositional relationship between the inlet of gas and the outlet ofexhaust. The space for reaction in the reaction chamber is defined bythe surface of the substrate (πr²) and the space between the upperelectrode and the lower electrode. Considering the gas flow through thespace for reaction, α can be estimated as ½. In the above formula, α is½.

Basic Effects

In this method, the material gas is, in short, a silicon-containinghydrocarbon compound including at least one Si-O bond, at most twoO—C_(n)H_(2n+1) bonds and at least two hydrocarbon radicals bonded tothe silicon (Si). Also, this material gas is vaporized by a directvaporization method. The method results in an insulation film having alow dielectric constant, high thermal stability and highhumidity-resistance.

More specifically, the material gas vaporized by the direct vaporizationmethod can stay in the plasma for a sufficient length of time. As aresult, a linear polymer can be formed so that a linear polymer havingthe basic structure (formula 7), wherein the “n” is 2 or a greatervalue, forms in a vapor phase. The polymer is then deposited on thesemiconductor substrate and forms an insulation film having a microporeporous structure.

wherein X1 and X2 are O_(n)C_(m)H_(p) wherein n is 0 or 1, m and p areintegers including zero.

The insulation film of this invention has a relatively high stabilitybecause its fundamental structure has the Si-O bond having high bondingenergy therebetween. Also, its dielectric constant is low because it hasa micropore porous structure. Further, the fundamental structure(—Si—O—)_(n) has, on both sides, dangling bonds ending with ahydrocarbon radical possessing hydrophobicity, and this property rendersthe humidity-resistance. Furthermore, the bond of a hydrocarbon radicaland silicon is generally stable. For instance, both the bond with amethyl radical, i.e., Si—CH₃, and bond with benzene, i.e., Si—C₆H₅, havea dissociation temperature of 500° C. or higher. Since abovesemiconductor production requires thermal stability to temperaturesabove 450° C., that property of the film is advantageous for productionof semiconductors.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description of the preferred examples whichfollows.

Outline of Example Structures

FIG. 1 diagrammatically shows a plasma CVD apparatus usable in thisinvention. This apparatus comprises a reaction gas-supplying device 12and a plasma CVD device 1. The reaction gas-supplying device 12comprises plural lines 13, control valves 8 disposed in the lines 13,and gas inlet ports 14, 15 and 16. A flow controller 7 is connected tothe individual control valves 8 for controlling a flow of a material gasof a predetermined volume. A container accommodating liquid reactingmaterial 18 is connected to a vaporizer 17 that directly vaporizesliquid. The plasma CVD device 1 includes a reaction chamber 6, a gasinlet port 5, a susceptor 3 and a heater 2. A circular gas diffusingplate 10 is disposed immediately under the gas inlet port. The gasdiffusing plate 10 has a number of fine openings at its bottom face andcan inject reaction gas to the semiconductor substrate 4 therefrom.There is an exhaust port 11 at the bottom of the reaction chamber 6.This exhaust port 11 is connected to an outer vacuum pump (not shown) sothat the inside of the reaction chamber 6 can be evacuated. Thesusceptor 3 is placed in parallel with and facing the gas diffusingplate 10. The susceptor 3 holds a semiconductor substrate 4 thereon andheats it with the heater 2. The gas inlet port 5 is insulated from thereaction chamber 6 and connected to an outer high frequency power supply9. Alternatively, the susceptor 3 can be connected to the power supply9. Thus, the gas diffusing plate 10 and the susceptor 3 act as a highfrequency electrode and generate a plasma reacting field in proximity tothe surface of the semiconductor substrate 4.

A method for forming an insulation film on a semiconductor substrate byusing the plasma CVD apparatus of this invention comprises a step ofdirectly vaporizing silicon-containing hydrocarbon compounds expressedby the general formula Si_(α)O_(β)C_(x)H_(y) (α, β, x, and y areintegers) and then introducing it to the reaction chamber 6 of theplasma CVD device 1, a step of introducing an additive gas, whose flowis substantially reduced, into the reaction chamber 6 and also a step offorming an insulation film on a semiconductor substrate by plasmapolymerization reaction wherein mixed gases, made from thesilicon-containing hydrocarbon compound as a material gas and theadditive gas, are used as a reaction gas. It is a remarkable featurethat the reduction of the additive gas flow also renders a substantialreduction of the total flow of the reaction gas. This feature will bedescribed in more detail later.

Material Gas and Additive Gas

In this regard, the silicon-containing hydrocarbon compound expressed asthe general formula Si_(α)O_(β)C_(x)H_(y) (α, β, x, and y are integers)is preferably a compound having at least one Si—O bond, two or lessO—C_(n)H₂₊₁ bonds and at least two hydrocarbon radicals bonded withsilicon (Si). More specifically, it is a compound indicated by (A)chemical formula:

wherein R1 and R2 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, and m and nare any integers;

a compound indicated by

(B) chemical formula:

wherein R1, R2 and R3 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, and nis any integer;

a compound indicated by

(C) chemical formula:

wherein R1, R2, R3 and R4 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ and C₆H₅, andm and n are any integer;

a compound indicated by

(D) chemical formula:

wherein R1, R2, R3, R4, R5 and R6 are one of CH₃, C₂H₃, C₂H₅, C₃H₇ andC₆H₅, and a mixture of the compound with nitrogen oxide (N₂O) or oxygen(O₂) as an oxidizing agent; or

a compound indicated by

(E) chemical formula:

wherein R1, R2, R3 and R4 are one of CH₃, C₂H₃, C₂H1, C3H₇ and C₆H₅, anda mixture of the compound with nitrogen oxide (N₂O) or oxygen (O₂) as anoxidizing agent.

Further, it should be noted that the silicon-containing hydrocarboncompound can be any combinations of these compounds and mixtures.

The additive gases used in this embodiment, more specifically, are argongas and helium gas. Argon is principally used for stabilizing plasma,while helium is used for improving uniformity of the plasma and alsouniformity of thickness of the insulation film.

In the method described above, the first step of direct vaporization isa method wherein a liquid material, the flow of which is controlled, isinstantaneously vaporized at a vaporizer that is preheated. This directvaporization method requires no carrier gas such as argon to obtain adesignated amount of the material gas. This differs greatly with thebabbling method. Accordingly, a large amount of argon gas or helium gasis no longer necessary and this reduces the total gas flow of thereaction gas and then lengthens the time in which the material gas staysin the plasma. As a result, sufficient polymerizing reactions occur inthe vapor so that a linear polymer can be formed and a film having amicropore porous structure can be obtained.

In FIG. 1, inert gas supplied through the gas inlet port 14 pushes outthe liquid reacting material 18, which is the silicon-containinghydrocarbon compound, to the control valve 8 through the line 13. Thecontrol valve 8 controls the flow of the liquid reacting material 18with the flow controller 7 so that it does not exceed a predeterminedvolume. The reduced silicon-containing hydrocarbon compound 18 goes tothe vaporizer 17 to be vaporized by the direct vaporization methoddescribed above. Argon and helium are supplied through the inlet ports15 and 16, respectively, and the valve 8 controls the flow volume ofthese gases. The mixture of the material gas and the additive gases,which is a reaction gas, is then supplied to the inlet port 5 of theplasma CVD device 1. The space between the gas diffusing plate 10 andthe semiconductor substrate 4, both located inside of the reactionchamber 6 which is already evacuated, is charged with high frequency RFvoltages, which are preferably 13.4 MHz and 430 kHz, and the spaceserves as a plasma field. The susceptor 3 continuously heats thesemiconductor substrate 4 with the heater 2 and maintains the substrate4 at a predetermined temperature that is desirably 350-450° C. Thereaction gas supplied through the fine openings of the gas diffusingplate 10 remains in the plasma field in proximity to the surface of thesemiconductor substrate 4 for a predetermined time.

If the residence time is short, a linear polymer cannot be depositedsufficiently so that the film deposited on the substrate does not form amicropore porous structure. Since the residence time is inverselyproportional to the flow volume of the reaction gas, a reduction of theflow volume of the reaction gas can lengthen its residence time.

Extremely reducing the total volume of the reaction gas is effected byreducing the flow volume of the additive gas. As a result, the residencetime of the reaction gas can be lengthened so that a linear polymer isdeposited sufficiently and subsequently an insulation film having amicropore porous structure can be formed.

In order to adjust the reaction in the vapor phase, it is effective toadd a small amount of an inert gas, an oxidizing agent, or a reducingagent to the reaction chamber. Helium (He) and Argon (Ar) are inertgases and have different first ionization energies of 24.56 eV and 15.76eV, respectively. Thus, by adding either He or Ar singly or both incombination in predetermined amounts, the reaction of the material gasin the vapor phase can be controlled. Molecules of the reaction gasundergo polymerization in the vapor phase, thereby forming oligomers.The oligomers are expected to have a O:Si ratio of 1:1. However, whenthe oligomers form a film on the substrate, the oligomers undergofurther polymerization, resulting in a higher oxygen ratio. The ratiovaries depending on the dielectric constant or other characteristics ofa film formed on the substrate (e.g., in Example 5 described later, theratio was 3:2).

The remaining oxygen, which is derived from the material gas and is notincorporated into the film, is dissociated from the material compoundand floats in plasma. The ratio of Si:O in the material gas variesdepending upon the compound. For example, in formulae 2-6 above, theratio of O:Si is 2:1, 1:1, 3:2, 1:2, and 0:1, respectively. If thematerial gas having a high ratio of O:Si (e.g., 3/2 or higher) is used,the quantity of oxygen floating in plasma increases. When the quantityof oxygen increases, the organic groups, which are directly bound to Siand necessary to form a film, are oxidized, and as a result,deterioration of the film is likely to occur. In the above, by adding areducing agent such as H₂ and CH₄ to the reaction chamber, the oxygenpartial pressure in plasma is reduced, thereby preventing the aboveoxidization of the organic groups. In contrast, when the O:Si ratio islow (e.g., 3/2 or lower), it is necessary to supply oxygen for forming afilm by adding an oxidizing agent such as N₂O and O₂. The appropriateamount of a reducing agent or an oxidizing agent can be evaluated inadvance based on preliminary experiment in which the composition of aformed film is analyzed by FT-IR or XRS, and its dielectric constant isalso analyzed. Accordingly, by selecting the appropriate type ofadditive gas such as He, Ar, a reducing agent, and an oxidizing agent,and by controlling the quantity of each gas to be added, a film havingthe desired quality can be produced.

Other Aspects

In the above, the silicon-containing hydrocarbon compound to produce amaterial gas for silicone polymer has preferably two alkoxy groups orless or having no alkoxy group. The use of a material gas having threeor more alkoxy groups interferes with formation of linear siliconepolymer, resulting in relatively high dielectric constant of a film. Inthe above, one molecule of the compound preferably contains one, two, orthree Si atoms, although the number of Si atoms is not limited (the morethe Si atoms, the vaporization becomes more difficult, and the cost ofsynthesis of the compound becomes higher). The alkoxy group may normallycontain 1-3 carbon atoms, preferably one or two carbon atoms.Hydrocarbons bound to Si have normally 1-12 carbon atoms, preferably 1-6carbon atoms. A preferable silicon-containing hydrocarbon compound hasformula:

Si_(α)O_(α-1)R_(2α-β+2)(OC_(n)H_(2n+1)) _(β)

wherein α is an integer of 1-3, β is 0, 1, or 2, n is an integer of 1-3,and R is C₁₋₆ hydrocarbon attached to Si. The use of an oxidizing agentor a reducing agent is determined depending on the target dielectricconstant (3.30 or less, preferably 3.10 or less, more preferably 2.80 orless) of a silicone polymer film and other characteristics such asstability of dielectric constant and thermal stability. The O:Si ratioin the material gas is also considered to select an oxidizing agent or areducing agent, as described above. Preferably, if the ratio is lowerthan 3:2, an oxidizing agent is used, whereas if the ratio is higherthan 3:2, a reducing agent is used. Further, an inert gas such as Ar andHe is for controlling plasma reaction, but is not indispensable to forma silicone polymer film. The flow of material gas and the flow ofadditive gas can also vary depending on the plasma CVD apparatus. Theappropriate flow can be determined by correlating the dielectricconstant of the silicone polymer film with the residence time of thereaction gas (composed of the material gas and the additive gas). Thelonger the residence time, the lower the dielectric constant becomes. Areduction rate of dielectric constant per lengthened residence time ischangeable, and after a certain residence time, the reduction rate ofdielectric constant significantly increases, i.e., the dielectricconstant sharply drops after a certain residence time of the reactiongas. After this dielectric constant dropping range, the reduction ofdielectric constant slows down. This is very interesting. In the presentinvention, by lengthening residence time until reaching the dielectricconstant dropping range based on a predetermined correlation between thedielectric constant of the film and the residence time of the reactiongas, it is possible to reduce the dielectric constant of the siliconepolymer film significantly.

EXAMPLES

Some preferred results in the experiments are described below. In theseexperiments, PM-DMOS (phenylmethyl dimethoxysilane, formula 1), DM-DMOS(dimethyl dimethoxysilane, formula 8), and P-TMOS were used as thematerial gas. An ordinary plasma CVD device (EAGLE-10™, ASM Japan K.K.)was used as an experimental device. The conditions for forming the filmare as follows;

Additive gas: Ar and He

RF power supply: 250W (use the frequency made from 13.4 MHz and 430 kHzby synthesizing them with each other)

Substrate temperature: 400° C.

Reacting pressure: 7 Torr

Vaporizing method: direct vaporization

The residence time (Rt) is defined with the following formula.

Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F

In this formula, each abbreviation indicates the following parameter.

Pr: reaction chamber pressure (Pa)

Ps: standard atmospheric pressure (Pa)

Tr: average temperature of the reaction gas (K)

Ts: standard temperature (K)

r_(w): radius of the silicon substrate (m)

d: space between the silicon substrate and the upper electrode (m)

F: total flow volume of the reaction gas (sccm)

Individual parameters were fixed at the following values; only the flowvolume was varied so as to find out the relationship between the flowvolume and the dielectric constant.

Pr=9.33×10² (Pa)

Ps=1.01×10⁵ (Pa)

Tr=273+400=673 (K)

Ts=273 (K)

r_(w)=0.1 (m)

d=0.014 (m)

Table 1 lists comparative examples and present invention's examples.

TABLE 1 Material Reaction Gas Gas Total Flow Ar He Flow Rt Dielectric(sccm) (sccm) (sccm) (sccm) (msec) constant ε C.Ex. 1 100 1000 1000 210024 3.38 (P-TMOS) C.Ex. 2 100 10 10 120 412 3.42 (P-TMOS) C.Ex. 3 100 775775 1650 30 3.41 (PM- DMOS) C.Ex. 4 100 550 550 1200 41 3.41 (PM- DMOS)C.Ex. 5 100 430 430 960 51 3.40 (PM- DMOS) C.Ex. 6 100 310 310 720 683.35 (PM- DMOS) Ex. 1 100 140 140 480 103 3.10 (PM- DMOS) Ex. 2 100 100100 300 165 2.76 (PM- DMOS) Ex. 3 100 70 70 240 206 2.64 (PM- DMOS) Ex.4 100 10 10 120 412 2.45 (PM- DMOS) Ex. 5 100 10 10 120 412 2.58 (DM-DMOS) Ex. 6 25 3 0 28 1764 2.51 (DM- DMOS) Ex. 7 25 0 5 30 1647 2.50(DM- DMOS) Additive H₂ CH₄ Gas (sccm) (sccm) Change Ex. 8 100 20 0 120412 2.52 (DM- DMOS) Ex. 9 25 5 0 30 1647 2.49 (DM- DMOS) Ex. 10 25 0 530 1647 2.67 (DM- DMOS)

Comparative Example 1

Material gas: P-TMOS (100 sccm)

Additive gases: Ar (1000 sccm) and He (1000 sccm)

Total flow volume of reaction gas: 2100 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 24 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 3.38.

Comparative Example 2

Material gas: P-TMOS (100 sccm)

Additive gases: Ar (10 sccm) and He (10 sccm)

Total flow volume of reaction gas: 120 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 412 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 3.42.

Comparative Example 3

Material gas: PM-DMOS (100 sccm)

Additive gases: Ar (775 sccm) and He (775 sccm)

Total flow volume of reaction gas: 1650 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 30 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 3.41.

Comparative Example 4

Material gas: PM-DMOS (100 sccm)

Additive gases: Ar (550 sccm) and He (550 sccm)

Total flow volume of reaction gas: 1200 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 41 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 3.41.

Comparative Example 5

Material gas: PM-DMOS (100 sccm)

Additive gas: Ar (430 sccm) and He (430 sccm)

Total flow volume of reaction gas: 960 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 51 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 3.40.

Comparative Example 6

Material gas: PM-DMOS (100 sccm)

Additive gases: Ar (310 sccm) and He (310 sccm)

Total flow volume of reaction gas: 720 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 68 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 3.35.

Example 1

Material gas: PM-DMOS (100 sccm)

Additive gases: Ar (140 sccm) and He (140 sccm)

Total flow volume of reaction gas: 480 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 103 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 3.10.

Example 2

Material gas: PM-DMOS (100 sccm)

Additive gases: Ar (100 sccm) and He (100 scem)

Total flow volume of reaction gas: 300 scem

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 165 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.76.

Example 3

Material gas: PM-DMOS (100 sccm)

Additive gases: Ar (70 sccm) and He (70 sccm)

Total flow volume of reaction gas: 240 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 206 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.64.

Example 4

Material gas: PM-DMOS (100 sccm)

Additive gases: Ar (10 sccm) and He (10 sccm)

Total flow volume of reaction gas: 120 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 412 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.45.

Hereinafter, the results given above will be examined with reference toFIGS. 2 and 3. FIG. 2 is a graph showing the relationship between thedielectric constant ε and the total flow volume of the reaction gas aswell as the relationship between the residence time Rt and the totalflow volume of the reaction gases, in the experiments using PM-DMOS as amaterial gas. FIG. 3 is a graph showing the relationship between theresidence time Rt and the dielectric constant ε in the experiments usingPM-DMOS as a material gas.

First, the relationship between the flow volume of the PM-DMOS gases andthe dielectric constant ε of the insulation film will be examined. FIG.2 shows that the dielectric constant ε is almost constantly 3.4 whilethe flow volume is about 700 sccm. However, the dielectric constant εbegins to fall with the decrease of the flow volume, i.e., atapproximately 700 sccm or less. Further, as the flow volume falls tounder 500 sccm, the residence time Rt rises drastically and thedielectric constant ε falls drastically. Meanwhile, FIG. 3 shows thatthe dielectric constant ε begins to decrease when the residence time Rtincreases from approximately 70 msec. When the residence time Rt isgreater than 400 msec, the dielectric constant ε falls to 2.45.

Thus, these present invention's examples apparently indicate that if thetotal flow of the reaction gas of the PM-DMOS gas and the additive gasis controlled so that Rt is more than 100 msec the dielectric constant εcan be controlled to be less than 3.1.

Example 5

DM-DMOS (formula 8) was then tested.

Material gas: DM-DMOS (100 sccm)

Additive gases: Ar (10 sccm) and He (10 sccm)

Total flow volume of reaction gas: 120 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 412 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.58.

Example 6

Material gas: DM-DMOS (25 sccm)

Additive gases: Ar (3 sccm) and He (0 sccm)

Total flow volume of reaction gas: 28 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 1764 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.51.

Example 7

Material gas: DM-DMOS (25 sccm)

Additive gases: Ar (0 sccm) and He (5 sccm)

Total flow volume of reaction gas: 30 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 1647 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.50.

Example 8

Material gas: DM-DMOS (100 sccm)

Additive gases: H₂ (20 sccm) and CH₄ (0 sccm)

Total flow volume of reaction gas: 120 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 412 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.52.

Example 9

Material gas: DM-DMOS (25 sccm)

Additive gases: H₂ (5 sccm) and CH₄ (0 sccm)

Total flow volume of reaction gas: 30 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 1647 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.49.

Example 10

Material gas: DM-DMOS (25 sccm)

Additive gases: H₂ (0 sccm) and CH₄ (5 sccm)

Total flow volume of reaction gas: 30 sccm

Other conditions and devices used for forming the film are given above.The calculated value of the residence time Rt was 1647 msec. Theconditions in this example reduced the dielectric constant ε of theinsulation film to 2.67.

Thus, the above reveals that, in the material gas of formula 2, bothcompounds (PM-DMOS having C₆H₅ at R1 and CH₃ at R2 and DM-DMOS havingCH₃ at R1 and CH₃ at R2) can produce insulation films having a very lowdielectric constant (ε<3.1).

The following will examine if the P-TMOS gas replacing the PM-DMOS gascan render the same results. Comparative Examples 1 and 2 both are theresults obtained in the experiments using the P-TMOS as a material gas.These examples indicate that the dielectric constant does not decreaseeven when the total flow of the reaction gas is reduced to 5.7%. Thus,the relationship between the flow volume and the dielectric constantthat is effected with PM-DMOS does not come into effect with P-TMOS.

Further, the following will examine differences of dielectric constantwhen using different material gases. Comparing Comparative Example 2with the present invention's Example 4, although the flow volumes andother conditions are identical, the dielectric constant ε of P-TMOS is3.42 while the dielectric constant ε of PM-DMOS is 2.45. Such a largedifference between the dielectric constant values resides in thedifference in the molecular structures of the material gases. That is,PM-DMOS has a pair of relatively unstable O—CH₃ bonds which are prone toseparation so that that polymerization reactions occur and a linearpolymer (formula 7) forms in a gaseous state. This polymer is depositedon a semiconductor substrate, forming a micropore porous structure andsubsequently the dielectric constant of the insulation film decreases.In contrast, because P-TMOS has three O—CH₃ bonds, its polymer is notdeposited linearly even though the residence time is lengthened.Accordingly, the deposited film does not have the micropore porousstructure nor such a low dielectric constant.

These experiments have revealed that it is preferable that thesilicon-containing hydrocarbon compounds used as the material gasesshould have not only the Si—O bonds but also at most two O—C_(n)H_(2n+1)bonds and, further, at least two hydrocarbon radicals bonded to thesilicon (Si).

Film stability characteristics of low dielectric constant films formedaccording to the present invention were evaluated by preparing lowdielectric constant films according to Example 4, wherein PM-DMOS wasused, and Example 5, wherein DM-DMOS was used, thereby evaluating theirstability of dielectric constant and their thermal stability.

(1) Stability of Dielectric constant

Changes in dielectric constant of the films were measured upon heatingand humidifying the PM-DMOS film and the DM-DMOS film in a pressurecooker. That is, each film was formed on a Si wafer at a thickness of 1μm, and its dielectric constant was measured upon formation of the filmand after being placed at 120° C. and 100% humidity for one hour. Theresults are shown below. No change in dielectric constant of each filmwas detected, i.e., indicating high stability characteristics.

TABLE 2 Dielectric constant One Hour at High Material Gas Upon FormationTemp. and Humid. Example 4 PM-DMOS 2.45 2.45 Example 5 DM-DMOS 2.58 2.58

(2) Thermal Stability

Based on a thermal desorption test, thermal stability of film structureswas evaluated. That is, the samples of PM-DMOS formed on the Si waferand DM-DMOS formed on the Si wafer were placed in a vacuum and subjectedto rising temperature at a rate of 10° C. per minute, thereby measuringthe amount of molecules dissociated from the film. FIG. 4 is a graphshowing the thermal desorption spectra of components having a molecularweight of 16 due to desorption of CH₄ during the temperature rise. FIG.5 is a graph showing changes in the degree of vacuum corresponding tothe number of total molecules dissociated from the film. In bothexperiments, no desorption was detected in either film at a temperatureof 400° C. or lower. Desorption began at approximately 450° C. inPM-DMOS and at approximately 500° C. in DM-DMOS. Thermal stabilityrequired for low dielectric constant films is generally for 400° C. to450° C. Therefore, it was proved that both the PM-DMOS film and theDM-DMOS film had high thermal stability.

As described above, the method of this invention using thesilicon-containing hydrocarbon compounds of this invention as thematerial gases produces an insulation film that has high thermalstability, high humidity-resistance and a low dielectric constant.Additionally, it is found that controlling the residence time of thereaction gas can effectively and easily control the dielectric constantof the film. Further, the method of this invention actualizes easyproduction of insulation films without using expensive devices.

Although this invention has been described in terms of certain examples,other examples apparent to those of ordinary skill in the art are withinthe scope of this invention. Accordingly, the scope of the invention isintended to be defined only by the claims that follow.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

What is claimed is:
 1. A method for forming a siloxan polymer insulationfilm on a semiconductor substrate by plasma treatment, comprising thesteps of: vaporizing a silicon-containing hydrocarbon compound toproduce a material gas for silicone polymer, said silicon-containinghydrocarbon having the formulaSi_(α)O_(α−1)R_(2α−β+2)(OC_(n)H_(2n+1))_(β) wherein α is an integer of1-3, β is 0, 1, or 2, n is an integer of 1-3, and R is C₁₋₆ hydrocarbonattached to Si; introducing the material gas into a reaction chamber forplasma CVD processing wherein a semiconductor substrate is placed;introducing an additive gas comprising an inert gas and optionally anoxidizing gas, said oxidizing gas being used in an amount less than thematerial gas; and forming a siloxan polymer film having —SiR₂O—repeating structural units on the semiconductor substrate by activatingplasma polymerization reaction in the reaction chamber where a reactiongas composed of the material gas and the additive gas is present, whilecontrolling the flow of the reaction gas to lengthen a residence time,Rt, of the reaction gas in the reaction chamber, wherein 100 msec≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F wherein: Pr: reaction chamberpressure (Pa) Ps: standard atmospheric pressure (Pa) Tr: averagetemperature of the reaction gas (K) Ts: standard temperature (K) r_(w):radius of the silicon substrate (m) d: space between the siliconsubstrate and the upper electrode (m) F: total flow volume of thereaction gas (sccm).
 2. The method according to claim 1, wherein theresidence time is determined by correlating the dielectric constant withthe residence time.
 3. The method according to claim 1, wherein theadditive gas comprises at least either argon (Ar) or Helium (He).
 4. Themethod according to claim 1, wherein the flow of the reaction gas iscontrolled to render the relative dielectric constant of the siliconepolymer film lower than 3.30.
 5. The method according to claim 1,wherein the flow of the reaction gas is controlled to render thedielectric constant of the silicone polymer film no more than 3.1. 6.The method according to claim 1, wherein Rt is no less than 165 msec. 7.The method according to claim 1, wherein the additive gas is exclusivelyan inert gas.
 8. A method for forming a siloxan polymer insulation filmon a semiconductor substrate by plasma treatment, comprising the stepsof: vaporizing a silicon-containing hydrocarbon compound to produce amaterial gas for silicone polymer, said silicon-containing hydrocarbonhaving the formula Si_(α)O_(α−1)R_(2α−β+2)(OC_(n)H_(2n+1))_(β) wherein αis an integer of 1-3, β is 0 or 1, n is an integer of 1-3, and R is C₁₋₆hydrocarbon attached to Si; introducing the material gas into a reactionchamber for plasma CVD processing wherein a semiconductor substrate isplaced; introducing an additive gas comprising an inert gas and anoxidizing gas, said oxidizing gas being used in an amount less than thematerial gas; and forming a siloxan polymer film having —SiR₂O—repeating structural units on the semiconductor substrate by activatingplasma polymerization reaction in the reaction chamber where a reactiongas composed of the material gas and the additive gas is present, whilecontrolling the flow of the reaction gas to lengthen a residence time,Rt, of the reaction gas in the reaction chamber, wherein 100 msec≦Rt,Rt[s]=9.42×10⁷(Pr·Ts/Ps·Tr)r_(w) ²d/F wherein: Pr: reaction chamberpressure (Pa) Ps: standard atmospheric pressure (Pa) Tr: averagetemperature of the reaction gas (K) Ts: standard temperature (K) r_(w):radius of the silicon substrate (m) d: space between the siliconsubstrate and the upper electrode (m) F: total flow volume of thereaction gas (sccm).
 9. A method for forming a siloxan polymerinsulation film on a semiconductor substrate by plasma treatment,comprising the steps of: vaporizing a silicon-containing hydrocarboncompound to produce a material gas for silicone polymer, saidsilicon-containing hydrocarbon having the general formulaSi_(α)O_(β)C_(x)H_(y) wherein α,β,x, and y are integers; introducing thematerial gas into a reaction chamber for plasma CVB processing wherein asemiconductor substrate is placed; introducing an additive gas; andforming a siloxan polymer film having −SiR₂O− repeatin structural unitson the semiconductor substrate by activating plasma polymerization inthe reaction chamber where a reaction gas composed of the material gasand the additive gas is present, while controlling the flow of thereaction gas to lenghthen a residence time, Rt, of the reaction gas inthe reaction chamber, wherein 100 msec≦Rt, Rt=9.42×10⁷(Pr.Ts/Ps.Tr)r_(w)²d/f wherein: Pr: reaction chamber pressure (Pa) Ps: standardatmospheric pressure (Pa) Tr: average temperature of the reaction gas(K) Ts: standard temperature (K) r_(w): radius of the silicon substrate(m) d: space between the silicon substrate and the upper electrode (m)F: total flow volume of the reaction gas (sccm).
 10. The methodaccording to claim 9, wherein the alkoxy present in thesilicon-containing hydrocarbon compound has 1 to 3 carbon atoms.
 11. Themethod according to claim 9, wherein the hydrocarbon present in thesilicon-containing hydrocarbon compound has 1 to 6 carbon atoms.
 12. Themethod according to claim 9, wherein the silicon-containing hydrocarboncompound has 1 to 3 silison atoms.
 13. The method according to claim 9,wherein the silicon-containing hydrocarbon compound has formulaSi_(α)O_(α-1)R_(2αβ+2)(OC_(n)H_(2n+1))_(β) wherein α is an integer of1-3, β is 0, 1,or 2, n is an integer of 1-3, and R is C₁₋₆ hydrocarbonattached Si.
 14. The method according to claim 9, wherein the additivegas comprises at least either argon (Ar) or Helium (He).
 15. The methodaccording to claim 9, wherein the additive gas comprises either anoxidizing agent or a reducing agent.
 16. The method according to claim14, wherein the additive gas further comprises either an oxidizing agentor a reducing agent.
 17. The method according to claim 9, wherein thesilicon-containing hydrocarbon compound is selected from the groupconsisting of:

wherein R1 and R2 are independently CH₃, C₂H₃, C₂H₅, C₃H₇ or C₆H₅, and mand n are any integer,

wherein R1, R2 and R3 are independently CH₃, C₂H₃, C₂H₅, C₃H₇ or C₆H₅,and n is any integer,

wherein R1, R2, R3 and R4 are independently CH₃, C₂H₃, C₂H₅, C₃H₇ orC₆H₅, and m and n are any integer,

wherein R1, R2, R3, R4, R5 and R6 are independently CH₃, C₂H₃, C₂H₅,C₃H₇ or C₆H₅, ir the additive gases are argon (Ar), Helium (He) andeither nitrogen oxide (N₂O)or oxygen (O₂), and

wherein R1, R2, R3 and R4 are independently CH₃, C₂H₃, C₂H₅, C₃H₇ orC₆H₅, if the additive gases are argon (Ar), Helium (He) and eithernitrogen oxide (N₂O) or oxygen (O₂).
 18. The method according to claim9, wherein the flow of the reaction gas is controlled to render therelative dielectic constant of the silicone polymer film lower than3.30.